Chapter-7. Control and Coordination Science class 10 in english Medium CBSE Notes

Control and Coordination in Plants

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Control and coordination in plants are carried out by plant hormones, which are also called phytohormones. Different plant hormones help in coordinating growth, development and responses to the environment. They help plants respond appropriately to different stimuli such as light, gravity, water and touch.

Plants show two different types of movements-

(1)  Growth-independent movements - These movements do not depend on the growth of the plant. Such movements usually occur rapidly in response to a stimulus. For example, the folding or shrinking of the leaves of the touch-me-not plant (Mimosa pudica) when touched.

(2)  Growth-dependent movements -  These are the movements in plants that occur due to the growth of different parts of the plant body. Such movements are generally slow because they are associated with growth. Examples include the movement of tendrils, movement of a plant towards light and movement of roots towards water.

(1) Growth-independent Movement 

Movement in the Touch-me-not Plant - When we touch the touch-me-not plant (Mimosa pudica), it responds to the stimulus by showing movement in its leaves. The leaves fold or droop as a result of the touch. This movement is not related to growth because it occurs rapidly and does not involve the growth of the plant.

Immediate Response of Plants to a Stimulus - 

Plants also use electrochemical means to transmit information about touch from one cell to another. However, unlike animals, plants do not have any specialised tissues such as nerves for conducting information throughout the body. Plant cells also do not have specialised proteins like those found in animal muscle cells for producing movement. Instead, plant cells can change their shape by changing the amount of water inside them. As a result, the cells may swell or shrink, causing changes in the shape and position of different plant parts. This mechanism helps the touch-me-not plant show a rapid response when touched.

(2) Growth-dependent Movement 

(a) Movement of Tendrils -

Tendrils are thin, thread-like structures that help climbing plants to obtain support. When a tendril comes in contact with a support, the side away from the support grows faster than the side in contact with the support. This unequal growth causes the tendril to coil around the support. Thus, the movement of tendrils is a growth-dependent movement.

(b) Tropisms

   (i) Phototropism

Phototropism is the growth movement of a plant part in response to light. The shoot of a plant generally grows towards light and therefore shows positive phototropism, while roots generally grow away from light.

   (ii) Geotropism (Gravitropism)

Geotropism or gravitropism is the growth movement of a plant part in response to gravity. Roots generally grow towards gravity and show positive geotropism, whereas shoots generally grow away from gravity and show negative geotropism.

   (iii) Chemotropism

Chemotropism is the growth movement of a plant part in response to a chemical stimulus. For example, the growth of the pollen tube towards the ovule during fertilisation is an example of chemotropism.

   (iv) Hydrotropism

Hydrotropism is the growth movement of a plant part in response to water or moisture. Plant roots generally grow towards a source of water and therefore show positive hydrotropism. This helps plants obtain water necessary for their growth and survival.

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